1. Field of the Invention
The invention pertains to a method for producing subsurface markings in a transparent material body, wherein a pulsed laser beam is focused in the interior of the material body in such a way that the laser beam exceeds the destruction threshold of the material body at least in the respective focal point and a permanent marking is produced. Individual markings form a freely selectable internal engraving as a result of a relative movement between the laser beam and the material body.
2. The Prior Art
Methods of this type are generally known, for example, from U.S. Pat. No. 4,467,172 or German Patent No. DD 237 972 A3. U.S. Pat. No. 5,637,244 also pertains to such laser-based methods for producing an internal engraving in a material body. This material body may consist of glass such that an internal glass engraving is produced in this case. Naturally, it would also be possible to utilize plastic materials, e.g., as described in U.S. Pat. No. 4,092,518. The internal engraving may be produced in the interior of the material body one-dimensionally, two-dimensionally or even three-dimensionally. This depends on the relative movement between the laser beam and the material body.
In latter-mentioned U.S. Pat. No. 5,637,244, it was already attempted to change the optical appearance of the internal engraving composed of the individual markings by varying the size of the individual markings. This can be realized, in particular, by utilizing an optical unit for changing the focal length. Markings with a diameter in the range between 0.1 and 0.4 mm can be produced in this fashion. However, this method is associated with a significant constructive expenditure. In addition, the precision in producing the markings and the quality of their appearance leave much to be desired. The invention aims to eliminate all these disadvantages.